Energy Efficient Conductors With Reduced Thermal Knee Points and The Method of Manufacture Thereof

Abstract

The present invention relates to electrical conductors for electrical transmission and distribution with pre-stress conditioning of the strength member so that the conductive materials of aluminum, aluminum alloys, copper, copper alloys, or copper micro-alloys are mostly tension free or under compressive stress in the conductor, while the strength member is under tensile stress prior to conductor stringing, resulting in a lower thermal knee point in the conductor.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]The present application claims priority from U.S. Provisional Application Ser. No. 62 / 056,332 filed on Sep. 26, 2014 and from U.S. Provisional Application Ser. No. 62 / 148,915 filed on Apr. 17, 2014 which are each hereby incorporated herein by reference in their respective entirety.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to electrical conductors for electrical transmission and distribution with pre-stress conditioning. In particular, the present invention relates to electrical conductors with strength members such as fiber reinforced composites. More specifically, the present invention relies upon pre-stress conditioning of the strength member so that the conductive materials of aluminum, aluminum alloys, copper, copper alloys, or copper micro-alloys are mostly tension free or under compressive stress in the conductor, while the strength member is under tensile stress prior to conductor stringing, resulting in ...

AI Technical Summary

Benefits of technology

The patent describes a method for protecting and pre-tensioning high-temperature conductors in electric towers. The method involves using a protective coating called encapsulation material that can withstand high temperatures without exposing the strength members to high stress. The encapsulation material is applied to the strength members before they are joined to the conductor, allowing for effective thermal expansion and self-damping. The method also includes a pre-tensioning process that increases the strength of the conductor without adding excessive stress to the electric towers. The encapsulation material can be easily fitted with conventional fittings and provides long-term protection against corrosion and environmental factors. Overall, the method improves the safety and reliability of high-temperature conductors in electric towers.

Problems solved by technology

Until the conductor reaches above its thermal knee point, the conductor thermal expansion is substantially controlled by conductive material such as aluminum or copper with high thermal expansion coefficient, resulting in large sag, limiting the conductor's current carrying capacity, as shown in FIG. 1.

This tensioning process can be as long as 48 hours or more, and requires special device and extra labor time from linemen as the linemen have to revisit the towers for final deadending after the tensioning process.

However, Gap conductors are typically very expensive.

It is difficult to install, requiring special training and tools and significantly more labor time in the field.

Furthermore, since the conductor strength member is taking virtually all the load and it retracts inside the Gap conductor's aluminum layers if the conductor breaks, it is impossible to repair gap conductor in the field.

The entire conductor segment from deadend to deadend must be replaced and installed, resulting in costly delays in restoring electrical transmission.

The grease inside the gap conductor has being reported to leak out through the aluminum strands over time, staining objects under the power lines as well as corona noise due to water beading on conductor surface as a result of the hydrophobic greasy surface.

The grease in Gap conductor is also for protecting the steel wires from corrosion, and removal of the grease will result in compromised corrosion resistance of gap conductors.

When the conductor is wrapped in the take-up reel as typically done during conductor stranding manufacturing, the overlaying of these pre-stressed multi-strand conductors likely caused irreversible deformation of the annealed substantially loose / open aluminum strands in all the under layers of conductors.

These permanent deformation of aluminum strands will cause not only conductor birdcaging, but also localized deformed aluminum strands to break and causing hot spots and conductor failure during energized conductor operation.

The severely loose aluminum alloys strands posed same challenges.

The core in the conductor might be protected with a thin aluminum cladding in JPS approach for high temperature operation, however, the aluminum cladding on the core is also subjected to extreme tension as high as 190 MPa during the pre-stretching process of the core while aluminum strands are stranded, making it vulnerable to vibration fatigue.

The thin cladding is unable to sustain the tensioned core and minimize its shrinking inside the conductor that the ends of the conductor must be fixed before the tension in the core is released, forcing all the aluminum strands to be very loose.

The loose aluminum strands and the need to fix the conductor ends make it difficult to handle the conductors in both manufacturing and field stringing.

Pre-tensioning of ACSS does reduce thermal knee point and improve thermal sag, however, the high stress required in ACSS in tensioning increases risk to the safe operation of the transmission towers, especially for older transmission towers in reconductoring application projects.

It is uncommon for these conductors to be pre-stressed on existing towers as the older towers may not be capable of high level pre-tension required to substantially suppress conductor thermal knee point.

These composite core(s) are vulnerable to fiber buckling failure from excessive axial compressive stress during installation, such as the case in sharp angle situations associated with mishandling.

Conductors with smaller cores, with better bend flexibility, are ironically more vulnerable as these conductors do not require much bend stress to fail when subjected to sharp angle (with the aluminum strands in the stranded conductors, sliding to accommodate bending of the strength member), especially when tension on the composite strength member is absent.

Hardware costs for projects using such conductors sometimes are as high as 50% of total project cost, which is unacceptable, especially for cost sensitive applications such as lower voltage electrical distribution network.

Furthermore, these conductors must follow precisely prescribed stringing temperature and time duration, especially in bundled configurations during stringing, making the installation process prohibitively expensive.

If the tension and time history of the phase conductors are different, there could be different thermal knee points for each conductor and differential sagging among the bundled phase conductors after installation, causing flashing or even short circuits with changing conductor temperatures.

Such changes in conductor sag are not only substantial but also seemed random and unpredictable, a significant issue for field engineers and the electric utility.

Another challenge for conductors with carbon fiber polymeric composite core and annealed aluminum is their high sag in heavy ice environments.

This requires extra time and expensive effort from linemen.

This procedure will be unnecessary if a pre-tension treated conductor is used.

In electric distribution network, where it operates at lower voltage, conductors are subjected to higher current density due to cost constraints.

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